1. Technical Field
The present invention relates to the field of management of supply chain, more particularly of optimization of material flows in the batch process industry.
2. Background of Invention
In batch process industries, one of the key issues that must be well addressed by the scheduling system is its capability to handle the material flow between the different steps of the process. To define the strict relationship between two steps of a manufacturing process, where one of the steps produces as output an intermediate product or a material which is needed as input by the other step, the concept of “pegging” is often used. By using pegging arcs it is possible to define all those parameters (e.g. time and quantity) that rule the relationship between the two steps and related activities.
Traditionally there are two different approaches to the above issue:                Dynamic Pegging approach. In this approach, the scheduling system takes decisions on the sources and destinations of the material flow, on the quantities and when they are produced and consumed. All these decisions are inter-related and taken at the same time.        Static Pegging approach. Here the decisions on the sources and destinations of the material flow and the quantities are taken in a first step. Decisions regarding when the quantities are produced and consumed are taken in a second step.        
Dynamic Pegging approach is in theory a more advanced solution, however it might lead to models that are extremely hard to solve in a reasonable time. Indeed, the scheduling systems that use Dynamic Pegging are based on heuristics or use a simulation approach. Unfortunately these solving strategies bring poor schedules. For these reasons, the Static Pegging approach is often preferred, in particular when advanced optimization techniques are used.
State of the art scheduling systems that use a Static Pegging approach, normally transform the material flows into simple graph of precedence constraints between producing and consuming serialized activities. These approaches usually bring poor material synchronization when parallelism is possible. As an example, U.S. Pat. No. 7,426,418 discloses a method for supply chain planning by means of pegging arcs. In general, prior art systems which address this issue provide unsatisfactory results when a combination of serial and parallel production and/or consumption is required.